From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E8E5F3E4C74; Tue, 28 Apr 2026 10:06:19 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777370780; cv=none; b=O2cZ4X7u72eGypFIiRAg73vBSNSb8YJ4lygvKbHSrDnIda7AGsB0kOVW2pym1LgzqS49tbF5H8enw0dY2myolqqAc1J1uanfbE30DCiBpH52xWQnUt4msQtGln8jVMl28K3fcyBQ1oYXyMysGiOVlCOqAWAuYermGsr6yQ1f8e4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777370780; c=relaxed/simple; bh=AWfjFy1xojRQSJaJulb4Pm2bC+OIK+obMAqlpq0c018=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=Llv0YseyXPqvWD6Xn43YY6cNZs5BBYhozbL+rn9wbP9580NODDu7AbF+yhL6vaGdQXRzdmFAw0LI6poENMM9UuCWQi3Ks+usjonvqiR2oCnL4EML4QiktGyjeGopoz4m+hJ4LaGgIjt8+Q23Xs5nOrC0VR56nNnmN613MxiRgMo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=PmqFbsFU; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="PmqFbsFU" Received: by smtp.kernel.org (Postfix) with ESMTPSA id AE47BC2BCAF; Tue, 28 Apr 2026 10:06:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1777370779; bh=AWfjFy1xojRQSJaJulb4Pm2bC+OIK+obMAqlpq0c018=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=PmqFbsFUTG/9rSVRaADA2eVRe0zrojnWiuS374tRO6aCxI/ZVdQLX8e1K4i/nLlqN lIr6CMk1lESf0eWaX/A081nMU48DMCkU88urF9KIsBgowmy7H18VGxqIVfJsBXN6pn H28DoxSdOnPYxlU25pS0exa50Iph12eSYIJlEjUhTBijblJ2y4ZXFockuXxtRIe0Ag qTd/vWY+GZ/XvYlcvUreNQKnj7hp8muwIJRIEwIy3k03JqjI1wDW/ft3SzxkbBgmHo R4jLl9AG6Q1fNpjkfjYQ8m/d+Zo6P38xoFm2psivujM/hFsHbTNXSXkSBXJyfsiPGf 3M4Ix9DDhC7DA== Message-ID: <7f729e75-dd66-49ea-ab5f-408fdc1a5c81@kernel.org> Date: Tue, 28 Apr 2026 12:06:14 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] selftests/mm: khugepaged: initialize file contents via mmap To: Vineet Agarwal Cc: akpm@linux-foundation.org, ljs@kernel.org, shuah@kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org References: <3abf09d8-a98e-4f1b-b8d9-77879a8a2733@kernel.org> <20260428094356.60415-1-agarwal.vineet2006@gmail.com> <548dc617-ca19-45f6-852f-adebcf8d3a11@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 4/28/26 11:52, Vineet Agarwal wrote: > ftruncate() is needed before mmap(), since the file is created with > O_TRUNC and initially has size 0. Without resizing it first, mapping > and accessing the full range can go beyond EOF. Ah, that makes sense, worth spelling it out. Indeed, we otherwise get $ sudo ./khugepaged madvise:file . Save THP and khugepaged settings... OK Allocate huge page on fault... OK Split huge PMD on MADV_DONTNEED... OK Run test: collapse_full (madvise:file) Creating ./collapse_test_file for collapse...Bus error -- Cheers, David